P0171 on a 2013 Toyota Tacoma

P0171 means the engine computer is adding more fuel than normal on bank 1 because it sees too much air or not enough fuel.

Not your vehicle? See general P0171 info.

Most common causes on the 2013 Toyota Tacoma

Ranked from 124 NHTSA owner complaints filed for this vehicle.

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1
Secondary Air Injection System (SAIS) Valve Stuck Open
Medium severity
A stuck open secondary air injection valve allows unmetered air into the exhaust stream, which the oxygen sensor reads as a lean condition, triggering P0171. This is a known issue on this generation of Tacoma, often accompanied by codes like P2440 or a loss of power.
Reported in 2 NHTSA complaints
2
Low Fuel Pressure / Failing Fuel Pump
High severity
If the engine is not receiving adequate fuel pressure, the air-to-fuel ratio becomes lean. Symptoms can include a crank-no-start condition that temporarily resolves with starter fluid.
Reported in 1 NHTSA complaint
3
Dirty or Faulty Mass Air Flow (MAF) Sensor
Medium severity
A contaminated MAF sensor under-reports the amount of air entering the engine, causing the PCM to inject less fuel than needed. Inspect the sensor wire for dirt or oil buildup, especially if an aftermarket oiled air filter is used.
Common cause
4
Intake Manifold or Vacuum Leak
Medium severity
Unmetered air entering the engine past the MAF sensor leans out the air/fuel mixture. Look for cracked vacuum hoses, a loose intake boot, or leaking intake manifold gaskets.
Common cause
5
Faulty Upstream Air/Fuel Ratio (O2) Sensor
Medium severity
A degraded or failing upstream oxygen sensor (Bank 1, Sensor 1) can falsely report a lean condition to the engine computer. Confirm by checking live sensor data for sluggish voltage switching or a biased reading.
Common cause
6
Exhaust Leak Before the O2 Sensor
Medium severity
An exhaust leak near the manifold or upstream of the primary O2 sensor can draw ambient air into the exhaust stream via the Venturi effect. Listen for a ticking noise under load to confirm.
Common cause
7
Clogged or Restricted Fuel Injectors
Medium severity
Restricted injectors fail to deliver the commanded amount of fuel, resulting in a lean mixture on the affected bank. A cylinder drop test or injector balance test can help isolate the issue.
Common cause

These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0171 on your car still needs shop confirmation before any repair.

Common symptoms

Check engine light
Rough idle
Hesitation
Surging idle
Poor fuel economy

What to check before replacing parts

Review short- and long-term fuel trims on bank 1

Look for: High positive trims (commonly worse at idle, improving with RPM) mean the computer is adding fuel to compensate for excess air or insufficient fuel — that pattern is this code's fingerprint.

Smoke-test the intake

Look for: Smoke escaping (or a hiss you can hear) at intake boots, gaskets, or vacuum hose connections confirms unmetered air is entering after the MAF sensor, which is the most common cause of a lean code.

Inspect the PCV hoses and valve

Look for: A cracked, split, or disconnected PCV hose, or a PCV valve stuck open, draws in extra unmetered air the same way a vacuum leak does.

Clean and test the MAF sensor

Look for: Visible dirt or oil film on the sensor element, or a grams/second reading that doesn't track expected airflow for RPM, means the MAF is under-reporting air and causing the computer to under-fuel.

Verify fuel pressure

Look for: Pressure below spec (weak pump, clogged filter, failing regulator) starves the engine of fuel and produces the same lean trim pattern as a vacuum leak — rule it out before chasing leaks.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Car Runs Rough